This invention relates to reduction of aircraft wing wake and rotorcraft blade-vortex-interference.
In a rotorcraft airfoil, the concept of leading edge incident flow diversion to wing tip was proposed by Dancila in 2002. U.S. Pat. No. 6,948,906 (Leishman, et al) discloses a scheme of having at least one inlet located above the leading edge of a rotorcraft airfoil blade, where the leading edge incident air flow entering an arc-shaped tube through the inlet located above the leading edge and comes out as a jet from an outlet located at the blade tip side face. The air from the jet mixes with the blade vortex inner core and reduces blade vortex by as much as 60% in comparison to an unslotted baseline blade tip.
U.S. Pat. No. 6,948,906 does not disclose the implications of variations in locating the inlet either on the chord plane or between the chord plane and the upper surface of the rotorcraft airfoil blade. The study which led to the present invention suggests that in the conditions disclosed in U.S. Pat. No. 6,948,906, the inlet, instead of capturing the airfoil incident flow, functions as an outlet which vents the high-pressure rollup air at the tip side face to the low-pressure areas above the airfoil leading edge. The present state of technology does not offer a simple method to produce counter-rotating vortices without changing the airfoil outer shape or without the addition of wing-tip turbines. There is a great need to reduce blade and wing tip vortices without adding more form drag and mass to the blade or wing tip and without compromising strength.